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62c3711632
POSIX requires this to prevent entering function definitions in history but this implementation does nothing except retain the option's value. In ksh88, function definitions were usually entered in the history file, even when they came from ~/.profile and the $ENV file, to allow displaying their definitions. This is also the first option that does not have a letter.
2857 lines
72 KiB
Groff
2857 lines
72 KiB
Groff
.\"-
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.\" Copyright (c) 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Kenneth Almquist.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
|
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" from: @(#)sh.1 8.6 (Berkeley) 5/4/95
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.\" $FreeBSD$
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.\"
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.Dd August 29, 2015
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.Dt SH 1
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.Os
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.Sh NAME
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.Nm sh
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.Nd command interpreter (shell)
|
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.Sh SYNOPSIS
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.Nm
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.Op Fl /+abCEefhIimnPpTuVvx
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.Op Fl /+o Ar longname
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.Oo
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|
.Ar script
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.Op Ar arg ...
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.Oc
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.Nm
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|
.Op Fl /+abCEefhIimnPpTuVvx
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.Op Fl /+o Ar longname
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.Fl c Ar string
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.Oo
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|
.Ar name
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.Op Ar arg ...
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.Oc
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.Nm
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|
.Op Fl /+abCEefhIimnPpTuVvx
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.Op Fl /+o Ar longname
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|
.Fl s
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.Op Ar arg ...
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.Sh DESCRIPTION
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|
The
|
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.Nm
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|
utility is the standard command interpreter for the system.
|
|
The current version of
|
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.Nm
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|
is close to the
|
|
.St -p1003.1
|
|
specification for the shell.
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|
It only supports features
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|
designated by
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|
.Tn POSIX ,
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|
plus a few Berkeley extensions.
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|
This man page is not intended to be a tutorial nor a complete
|
|
specification of the shell.
|
|
.Ss Overview
|
|
The shell is a command that reads lines from
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|
either a file or the terminal, interprets them, and
|
|
generally executes other commands.
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|
It is the program that is started when a user logs into the system,
|
|
although a user can select a different shell with the
|
|
.Xr chsh 1
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|
command.
|
|
The shell
|
|
implements a language that has flow control constructs,
|
|
a macro facility that provides a variety of features in
|
|
addition to data storage, along with built-in history and line
|
|
editing capabilities.
|
|
It incorporates many features to
|
|
aid interactive use and has the advantage that the interpretative
|
|
language is common to both interactive and non-interactive
|
|
use (shell scripts).
|
|
That is, commands can be typed directly
|
|
to the running shell or can be put into a file,
|
|
which can be executed directly by the shell.
|
|
.Ss Invocation
|
|
.\"
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|
.\" XXX This next sentence is incredibly confusing.
|
|
.\"
|
|
If no arguments are present and if the standard input of the shell
|
|
is connected to a terminal
|
|
(or if the
|
|
.Fl i
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|
option is set),
|
|
the shell is considered an interactive shell.
|
|
An interactive shell
|
|
generally prompts before each command and handles programming
|
|
and command errors differently (as described below).
|
|
When first starting, the shell inspects argument 0, and
|
|
if it begins with a dash
|
|
.Pq Ql - ,
|
|
the shell is also considered a login shell.
|
|
This is normally done automatically by the system
|
|
when the user first logs in.
|
|
A login shell first reads commands
|
|
from the files
|
|
.Pa /etc/profile
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|
and then
|
|
.Pa .profile
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|
in a user's home directory,
|
|
if they exist.
|
|
If the environment variable
|
|
.Ev ENV
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|
is set on entry to a shell, or is set in the
|
|
.Pa .profile
|
|
of a login shell, the shell then subjects its value to parameter expansion
|
|
and arithmetic expansion and reads commands from the named file.
|
|
Therefore, a user should place commands that are to be executed only
|
|
at login time in the
|
|
.Pa .profile
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|
file, and commands that are executed for every shell inside the
|
|
.Ev ENV
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|
file.
|
|
The user can set the
|
|
.Ev ENV
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|
variable to some file by placing the following line in the file
|
|
.Pa .profile
|
|
in the home directory,
|
|
substituting for
|
|
.Pa .shrc
|
|
the filename desired:
|
|
.Pp
|
|
.Dl "ENV=$HOME/.shrc; export ENV"
|
|
.Pp
|
|
The first non-option argument specified on the command line
|
|
will be treated as the
|
|
name of a file from which to read commands (a shell script), and
|
|
the remaining arguments are set as the positional parameters
|
|
of the shell
|
|
.Li ( $1 , $2 ,
|
|
etc.).
|
|
Otherwise, the shell reads commands
|
|
from its standard input.
|
|
.Pp
|
|
Unlike older versions of
|
|
.Nm
|
|
the
|
|
.Ev ENV
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|
script is only sourced on invocation of interactive shells.
|
|
This
|
|
closes a well-known, and sometimes easily exploitable security
|
|
hole related to poorly thought out
|
|
.Ev ENV
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|
scripts.
|
|
.Ss Argument List Processing
|
|
All of the single letter options to
|
|
.Nm
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|
have a corresponding long name,
|
|
with the exception of
|
|
.Fl c
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|
and
|
|
.Fl /+o .
|
|
These long names are provided next to the single letter options
|
|
in the descriptions below.
|
|
The long name for an option may be specified as an argument to the
|
|
.Fl /+o
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|
option of
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|
.Nm .
|
|
Once the shell is running,
|
|
the long name for an option may be specified as an argument to the
|
|
.Fl /+o
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|
option of the
|
|
.Ic set
|
|
built-in command
|
|
(described later in the section called
|
|
.Sx Built-in Commands ) .
|
|
Introducing an option with a dash
|
|
.Pq Ql -
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|
enables the option,
|
|
while using a plus
|
|
.Pq Ql +
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|
disables the option.
|
|
A
|
|
.Dq Li --
|
|
or plain
|
|
.Ql -
|
|
will stop option processing and will force the remaining
|
|
words on the command line to be treated as arguments.
|
|
The
|
|
.Fl /+o
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|
and
|
|
.Fl c
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|
options do not have long names.
|
|
They take arguments and are described after the single letter options.
|
|
.Bl -tag -width indent
|
|
.It Fl a Li allexport
|
|
Flag variables for export when assignments are made to them.
|
|
.It Fl b Li notify
|
|
Enable asynchronous notification of background job
|
|
completion.
|
|
(UNIMPLEMENTED)
|
|
.It Fl C Li noclobber
|
|
Do not overwrite existing files with
|
|
.Ql > .
|
|
.It Fl E Li emacs
|
|
Enable the built-in
|
|
.Xr emacs 1
|
|
command line editor (disables the
|
|
.Fl V
|
|
option if it has been set;
|
|
set automatically when interactive on terminals).
|
|
.It Fl e Li errexit
|
|
Exit immediately if any untested command fails in non-interactive mode.
|
|
The exit status of a command is considered to be
|
|
explicitly tested if the command is part of the list used to control
|
|
an
|
|
.Ic if , elif , while ,
|
|
or
|
|
.Ic until ;
|
|
if the command is the left
|
|
hand operand of an
|
|
.Dq Li &&
|
|
or
|
|
.Dq Li ||
|
|
operator; or if the command is a pipeline preceded by the
|
|
.Ic !\&
|
|
keyword.
|
|
If a shell function is executed and its exit status is explicitly
|
|
tested, all commands of the function are considered to be tested as
|
|
well.
|
|
.Pp
|
|
It is recommended to check for failures explicitly
|
|
instead of relying on
|
|
.Fl e
|
|
because it tends to behave in unexpected ways,
|
|
particularly in larger scripts.
|
|
.It Fl f Li noglob
|
|
Disable pathname expansion.
|
|
.It Fl h Li trackall
|
|
A do-nothing option for
|
|
.Tn POSIX
|
|
compliance.
|
|
.It Fl I Li ignoreeof
|
|
Ignore
|
|
.Dv EOF Ap s
|
|
from input when in interactive mode.
|
|
.It Fl i Li interactive
|
|
Force the shell to behave interactively.
|
|
.It Fl m Li monitor
|
|
Turn on job control (set automatically when interactive).
|
|
A new process group is created for each pipeline (called a job).
|
|
It is possible to suspend jobs or to have them run in the foreground or
|
|
in the background.
|
|
In a non-interactive shell,
|
|
this option can be set even if no terminal is available
|
|
and is useful to place processes in separate process groups.
|
|
.It Fl n Li noexec
|
|
If not interactive, read commands but do not
|
|
execute them.
|
|
This is useful for checking the
|
|
syntax of shell scripts.
|
|
.It Fl P Li physical
|
|
Change the default for the
|
|
.Ic cd
|
|
and
|
|
.Ic pwd
|
|
commands from
|
|
.Fl L
|
|
(logical directory layout)
|
|
to
|
|
.Fl P
|
|
(physical directory layout).
|
|
.It Fl p Li privileged
|
|
Turn on privileged mode.
|
|
This mode is enabled on startup
|
|
if either the effective user or group ID is not equal to the
|
|
real user or group ID.
|
|
Turning this mode off sets the
|
|
effective user and group IDs to the real user and group IDs.
|
|
When this mode is enabled for interactive shells, the file
|
|
.Pa /etc/suid_profile
|
|
is sourced instead of
|
|
.Pa ~/.profile
|
|
after
|
|
.Pa /etc/profile
|
|
is sourced, and the contents of the
|
|
.Ev ENV
|
|
variable are ignored.
|
|
.It Fl s Li stdin
|
|
Read commands from standard input (set automatically
|
|
if no file arguments are present).
|
|
This option has
|
|
no effect when set after the shell has already started
|
|
running (i.e., when set with the
|
|
.Ic set
|
|
command).
|
|
.It Fl T Li trapsasync
|
|
When waiting for a child, execute traps immediately.
|
|
If this option is not set,
|
|
traps are executed after the child exits,
|
|
as specified in
|
|
.St -p1003.2 .
|
|
This nonstandard option is useful for putting guarding shells around
|
|
children that block signals.
|
|
The surrounding shell may kill the child
|
|
or it may just return control to the tty and leave the child alone,
|
|
like this:
|
|
.Bd -literal -offset indent
|
|
sh -T -c "trap 'exit 1' 2 ; some-blocking-program"
|
|
.Ed
|
|
.It Fl u Li nounset
|
|
Write a message to standard error when attempting
|
|
to expand a variable, a positional parameter or
|
|
the special parameter
|
|
.Va \&!
|
|
that is not set, and if the
|
|
shell is not interactive, exit immediately.
|
|
.It Fl V Li vi
|
|
Enable the built-in
|
|
.Xr vi 1
|
|
command line editor (disables
|
|
.Fl E
|
|
if it has been set).
|
|
.It Fl v Li verbose
|
|
The shell writes its input to standard error
|
|
as it is read.
|
|
Useful for debugging.
|
|
.It Fl x Li xtrace
|
|
Write each command
|
|
(preceded by the value of the
|
|
.Va PS4
|
|
variable subjected to parameter expansion and arithmetic expansion)
|
|
to standard error before it is executed.
|
|
Useful for debugging.
|
|
.It nolog
|
|
Another do-nothing option for
|
|
.Tn POSIX
|
|
compliance.
|
|
It only has a long name.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Fl c
|
|
option causes the commands to be read from the
|
|
.Ar string
|
|
operand instead of from the standard input.
|
|
Keep in mind that this option only accepts a single string as its
|
|
argument, hence multi-word strings must be quoted.
|
|
.Pp
|
|
The
|
|
.Fl /+o
|
|
option takes as its only argument the long name of an option
|
|
to be enabled or disabled.
|
|
For example, the following two invocations of
|
|
.Nm
|
|
both enable the built-in
|
|
.Xr emacs 1
|
|
command line editor:
|
|
.Bd -literal -offset indent
|
|
set -E
|
|
set -o emacs
|
|
.Ed
|
|
.Pp
|
|
If used without an argument, the
|
|
.Fl o
|
|
option displays the current option settings in a human-readable format.
|
|
If
|
|
.Cm +o
|
|
is used without an argument, the current option settings are output
|
|
in a format suitable for re-input into the shell.
|
|
.Ss Lexical Structure
|
|
The shell reads input in terms of lines from a file and breaks
|
|
it up into words at whitespace (blanks and tabs), and at
|
|
certain sequences of
|
|
characters called
|
|
.Dq operators ,
|
|
which are special to the shell.
|
|
There are two types of operators: control operators and
|
|
redirection operators (their meaning is discussed later).
|
|
The following is a list of valid operators:
|
|
.Bl -tag -width indent
|
|
.It Control operators:
|
|
.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
|
|
.It Li & Ta Li && Ta Li \&( Ta Li \&) Ta Li \en
|
|
.It Li ;; Ta Li ;& Ta Li \&; Ta Li \&| Ta Li ||
|
|
.El
|
|
.It Redirection operators:
|
|
.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
|
|
.It Li < Ta Li > Ta Li << Ta Li >> Ta Li <>
|
|
.It Li <& Ta Li >& Ta Li <<- Ta Li >| Ta \&
|
|
.El
|
|
.El
|
|
.Pp
|
|
The character
|
|
.Ql #
|
|
introduces a comment if used at the beginning of a word.
|
|
The word starting with
|
|
.Ql #
|
|
and the rest of the line are ignored.
|
|
.Pp
|
|
.Tn ASCII
|
|
.Dv NUL
|
|
characters (character code 0) are not allowed in shell input.
|
|
.Ss Quoting
|
|
Quoting is used to remove the special meaning of certain characters
|
|
or words to the shell, such as operators, whitespace, keywords,
|
|
or alias names.
|
|
.Pp
|
|
There are four types of quoting: matched single quotes,
|
|
dollar-single quotes,
|
|
matched double quotes, and backslash.
|
|
.Bl -tag -width indent
|
|
.It Single Quotes
|
|
Enclosing characters in single quotes preserves the literal
|
|
meaning of all the characters (except single quotes, making
|
|
it impossible to put single-quotes in a single-quoted string).
|
|
.It Dollar-Single Quotes
|
|
Enclosing characters between
|
|
.Li $'
|
|
and
|
|
.Li '
|
|
preserves the literal meaning of all characters
|
|
except backslashes and single quotes.
|
|
A backslash introduces a C-style escape sequence:
|
|
.Bl -tag -width xUnnnnnnnn
|
|
.It \ea
|
|
Alert (ring the terminal bell)
|
|
.It \eb
|
|
Backspace
|
|
.It \ec Ns Ar c
|
|
The control character denoted by
|
|
.Li ^ Ns Ar c
|
|
in
|
|
.Xr stty 1 .
|
|
If
|
|
.Ar c
|
|
is a backslash, it must be doubled.
|
|
.It \ee
|
|
The ESC character
|
|
.Tn ( ASCII
|
|
0x1b)
|
|
.It \ef
|
|
Formfeed
|
|
.It \en
|
|
Newline
|
|
.It \er
|
|
Carriage return
|
|
.It \et
|
|
Horizontal tab
|
|
.It \ev
|
|
Vertical tab
|
|
.It \e\e
|
|
Literal backslash
|
|
.It \e\&'
|
|
Literal single-quote
|
|
.It \e\&"
|
|
Literal double-quote
|
|
.It \e Ns Ar nnn
|
|
The byte whose octal value is
|
|
.Ar nnn
|
|
(one to three digits)
|
|
.It \ex Ns Ar nn
|
|
The byte whose hexadecimal value is
|
|
.Ar nn
|
|
(one or more digits only the last two of which are used)
|
|
.It \eu Ns Ar nnnn
|
|
The Unicode code point
|
|
.Ar nnnn
|
|
(four hexadecimal digits)
|
|
.It \eU Ns Ar nnnnnnnn
|
|
The Unicode code point
|
|
.Ar nnnnnnnn
|
|
(eight hexadecimal digits)
|
|
.El
|
|
.Pp
|
|
The sequences for Unicode code points are currently only useful with
|
|
UTF-8 locales.
|
|
They reject code point 0 and UTF-16 surrogates.
|
|
.Pp
|
|
If an escape sequence would produce a byte with value 0,
|
|
that byte and the rest of the string until the matching single-quote
|
|
are ignored.
|
|
.Pp
|
|
Any other string starting with a backslash is an error.
|
|
.It Double Quotes
|
|
Enclosing characters within double quotes preserves the literal
|
|
meaning of all characters except dollar sign
|
|
.Pq Ql $ ,
|
|
backquote
|
|
.Pq Ql ` ,
|
|
and backslash
|
|
.Pq Ql \e .
|
|
The backslash inside double quotes is historically weird.
|
|
It remains literal unless it precedes the following characters,
|
|
which it serves to quote:
|
|
.Pp
|
|
.Bl -column "XXX" "XXX" "XXX" "XXX" "XXX" -offset center -compact
|
|
.It Li $ Ta Li ` Ta Li \&" Ta Li \e Ta Li \en
|
|
.El
|
|
.It Backslash
|
|
A backslash preserves the literal meaning of the following
|
|
character, with the exception of the newline character
|
|
.Pq Ql \en .
|
|
A backslash preceding a newline is treated as a line continuation.
|
|
.El
|
|
.Ss Keywords
|
|
Keywords or reserved words are words that have special meaning to the
|
|
shell and are recognized at the beginning of a line and
|
|
after a control operator.
|
|
The following are keywords:
|
|
.Bl -column "doneXX" "elifXX" "elseXX" "untilXX" "whileX" -offset center
|
|
.It Li \&! Ta { Ta } Ta Ic case Ta Ic do
|
|
.It Ic done Ta Ic elif Ta Ic else Ta Ic esac Ta Ic fi
|
|
.It Ic for Ta Ic if Ta Ic then Ta Ic until Ta Ic while
|
|
.El
|
|
.Ss Aliases
|
|
An alias is a name and corresponding value set using the
|
|
.Ic alias
|
|
built-in command.
|
|
Wherever the command word of a simple command may occur,
|
|
and after checking for keywords if a keyword may occur, the shell
|
|
checks the word to see if it matches an alias.
|
|
If it does, it replaces it in the input stream with its value.
|
|
For example, if there is an alias called
|
|
.Dq Li lf
|
|
with the value
|
|
.Dq Li "ls -F" ,
|
|
then the input
|
|
.Pp
|
|
.Dl "lf foobar"
|
|
.Pp
|
|
would become
|
|
.Pp
|
|
.Dl "ls -F foobar"
|
|
.Pp
|
|
Aliases are also recognized after an alias
|
|
whose value ends with a space or tab.
|
|
For example, if there is also an alias called
|
|
.Dq Li nohup
|
|
with the value
|
|
.Dq Li "nohup " ,
|
|
then the input
|
|
.Pp
|
|
.Dl "nohup lf foobar"
|
|
.Pp
|
|
would become
|
|
.Pp
|
|
.Dl "nohup ls -F foobar"
|
|
.Pp
|
|
Aliases provide a convenient way for naive users to
|
|
create shorthands for commands without having to learn how
|
|
to create functions with arguments.
|
|
Using aliases in scripts is discouraged
|
|
because the command that defines them must be executed
|
|
before the code that uses them is parsed.
|
|
This is fragile and not portable.
|
|
.Pp
|
|
An alias name may be escaped in a command line, so that it is not
|
|
replaced by its alias value, by using quoting characters within or
|
|
adjacent to the alias name.
|
|
This is most often done by prefixing
|
|
an alias name with a backslash to execute a function, built-in, or
|
|
normal program with the same name.
|
|
See the
|
|
.Sx Quoting
|
|
subsection.
|
|
.Ss Commands
|
|
The shell interprets the words it reads according to a
|
|
language, the specification of which is outside the scope
|
|
of this man page (refer to the BNF in the
|
|
.St -p1003.2
|
|
document).
|
|
Essentially though, a line is read and if
|
|
the first word of the line (or after a control operator)
|
|
is not a keyword, then the shell has recognized a
|
|
simple command.
|
|
Otherwise, a complex command or some
|
|
other special construct may have been recognized.
|
|
.Ss Simple Commands
|
|
If a simple command has been recognized, the shell performs
|
|
the following actions:
|
|
.Bl -enum
|
|
.It
|
|
Leading words of the form
|
|
.Dq Li name=value
|
|
are stripped off and assigned to the environment of
|
|
the simple command
|
|
(they do not affect expansions).
|
|
Redirection operators and
|
|
their arguments (as described below) are stripped
|
|
off and saved for processing.
|
|
.It
|
|
The remaining words are expanded as described in
|
|
the section called
|
|
.Sx Word Expansions ,
|
|
and the first remaining word is considered the command
|
|
name and the command is located.
|
|
The remaining
|
|
words are considered the arguments of the command.
|
|
If no command name resulted, then the
|
|
.Dq Li name=value
|
|
variable assignments recognized in 1) affect the
|
|
current shell.
|
|
.It
|
|
Redirections are performed as described in
|
|
the next section.
|
|
.El
|
|
.Ss Redirections
|
|
Redirections are used to change where a command reads its input
|
|
or sends its output.
|
|
In general, redirections open, close, or
|
|
duplicate an existing reference to a file.
|
|
The overall format
|
|
used for redirection is:
|
|
.Pp
|
|
.D1 Oo Ar n Oc Ar redir-op file
|
|
.Pp
|
|
The
|
|
.Ar redir-op
|
|
is one of the redirection operators mentioned
|
|
previously.
|
|
The following gives some examples of how these
|
|
operators can be used.
|
|
Note that stdin and stdout are commonly used abbreviations
|
|
for standard input and standard output respectively.
|
|
.Bl -tag -width "1234567890XX" -offset indent
|
|
.It Oo Ar n Oc Ns Li > Ar file
|
|
redirect stdout (or file descriptor
|
|
.Ar n )
|
|
to
|
|
.Ar file
|
|
.It Oo Ar n Oc Ns Li >| Ar file
|
|
same as above, but override the
|
|
.Fl C
|
|
option
|
|
.It Oo Ar n Oc Ns Li >> Ar file
|
|
append stdout (or file descriptor
|
|
.Ar n )
|
|
to
|
|
.Ar file
|
|
.It Oo Ar n Oc Ns Li < Ar file
|
|
redirect stdin (or file descriptor
|
|
.Ar n )
|
|
from
|
|
.Ar file
|
|
.It Oo Ar n Oc Ns Li <> Ar file
|
|
redirect stdin (or file descriptor
|
|
.Ar n )
|
|
to and from
|
|
.Ar file
|
|
.It Oo Ar n1 Oc Ns Li <& Ns Ar n2
|
|
duplicate stdin (or file descriptor
|
|
.Ar n1 )
|
|
from file descriptor
|
|
.Ar n2
|
|
.It Oo Ar n Oc Ns Li <&-
|
|
close stdin (or file descriptor
|
|
.Ar n )
|
|
.It Oo Ar n1 Oc Ns Li >& Ns Ar n2
|
|
duplicate stdout (or file descriptor
|
|
.Ar n1 )
|
|
to file descriptor
|
|
.Ar n2
|
|
.It Oo Ar n Oc Ns Li >&-
|
|
close stdout (or file descriptor
|
|
.Ar n )
|
|
.El
|
|
.Pp
|
|
The following redirection is often called a
|
|
.Dq here-document .
|
|
.Bd -unfilled -offset indent
|
|
.Oo Ar n Oc Ns Li << Ar delimiter
|
|
.Ar here-doc-text
|
|
.Ar ...
|
|
.Ar delimiter
|
|
.Ed
|
|
.Pp
|
|
All the text on successive lines up to the delimiter is
|
|
saved away and made available to the command on standard
|
|
input, or file descriptor
|
|
.Ar n
|
|
if it is specified.
|
|
If the
|
|
.Ar delimiter
|
|
as specified on the initial line is quoted, then the
|
|
.Ar here-doc-text
|
|
is treated literally, otherwise the text is subjected to
|
|
parameter expansion, command substitution, and arithmetic
|
|
expansion (as described in the section on
|
|
.Sx Word Expansions ) .
|
|
If the operator is
|
|
.Dq Li <<-
|
|
instead of
|
|
.Dq Li << ,
|
|
then leading tabs
|
|
in the
|
|
.Ar here-doc-text
|
|
are stripped.
|
|
.Ss Search and Execution
|
|
There are three types of commands: shell functions,
|
|
built-in commands, and normal programs.
|
|
The command is searched for (by name) in that order.
|
|
The three types of commands are all executed in a different way.
|
|
.Pp
|
|
When a shell function is executed, all of the shell positional
|
|
parameters (except
|
|
.Li $0 ,
|
|
which remains unchanged) are
|
|
set to the arguments of the shell function.
|
|
The variables which are explicitly placed in the environment of
|
|
the command (by placing assignments to them before the
|
|
function name) are made local to the function and are set
|
|
to the values given.
|
|
Then the command given in the function definition is executed.
|
|
The positional parameters are restored to their original values
|
|
when the command completes.
|
|
This all occurs within the current shell.
|
|
.Pp
|
|
Shell built-in commands are executed internally to the shell, without
|
|
spawning a new process.
|
|
There are two kinds of built-in commands: regular and special.
|
|
Assignments before special builtins persist after they finish
|
|
executing and assignment errors, redirection errors and certain
|
|
operand errors cause a script to be aborted.
|
|
Special builtins cannot be overridden with a function.
|
|
Both regular and special builtins can affect the shell in ways
|
|
normal programs cannot.
|
|
.Pp
|
|
Otherwise, if the command name does not match a function
|
|
or built-in command, the command is searched for as a normal
|
|
program in the file system (as described in the next section).
|
|
When a normal program is executed, the shell runs the program,
|
|
passing the arguments and the environment to the program.
|
|
If the program is not a normal executable file
|
|
(i.e., if it does not begin with the
|
|
.Dq "magic number"
|
|
whose
|
|
.Tn ASCII
|
|
representation is
|
|
.Dq Li #! ,
|
|
resulting in an
|
|
.Er ENOEXEC
|
|
return value from
|
|
.Xr execve 2 )
|
|
but appears to be a text file,
|
|
the shell will run a new instance of
|
|
.Nm
|
|
to interpret it.
|
|
.Pp
|
|
Note that previous versions of this document
|
|
and the source code itself misleadingly and sporadically
|
|
refer to a shell script without a magic number
|
|
as a
|
|
.Dq "shell procedure" .
|
|
.Ss Path Search
|
|
When locating a command, the shell first looks to see if
|
|
it has a shell function by that name.
|
|
Then it looks for a
|
|
built-in command by that name.
|
|
If a built-in command is not found,
|
|
one of two things happen:
|
|
.Bl -enum
|
|
.It
|
|
Command names containing a slash are simply executed without
|
|
performing any searches.
|
|
.It
|
|
The shell searches each entry in the
|
|
.Va PATH
|
|
variable
|
|
in turn for the command.
|
|
The value of the
|
|
.Va PATH
|
|
variable should be a series of
|
|
entries separated by colons.
|
|
Each entry consists of a
|
|
directory name.
|
|
The current directory
|
|
may be indicated implicitly by an empty directory name,
|
|
or explicitly by a single period.
|
|
.El
|
|
.Ss Command Exit Status
|
|
Each command has an exit status that can influence the behavior
|
|
of other shell commands.
|
|
The paradigm is that a command exits
|
|
with zero for normal or success, and non-zero for failure,
|
|
error, or a false indication.
|
|
The man page for each command
|
|
should indicate the various exit codes and what they mean.
|
|
Additionally, the built-in commands return exit codes, as does
|
|
an executed shell function.
|
|
.Pp
|
|
If a command is terminated by a signal, its exit status is greater than 128.
|
|
The signal name can be found by passing the exit status to
|
|
.Li kill -l .
|
|
.Pp
|
|
If there is no command word,
|
|
the exit status is the exit status of the last command substitution executed,
|
|
or zero if the command does not contain any command substitutions.
|
|
.Ss Complex Commands
|
|
Complex commands are combinations of simple commands
|
|
with control operators or keywords, together creating a larger complex
|
|
command.
|
|
More generally, a command is one of the following:
|
|
.Bl -item -offset indent
|
|
.It
|
|
simple command
|
|
.It
|
|
pipeline
|
|
.It
|
|
list or compound-list
|
|
.It
|
|
compound command
|
|
.It
|
|
function definition
|
|
.El
|
|
.Pp
|
|
Unless otherwise stated, the exit status of a command is
|
|
that of the last simple command executed by the command,
|
|
or zero if no simple command was executed.
|
|
.Ss Pipelines
|
|
A pipeline is a sequence of one or more commands separated
|
|
by the control operator
|
|
.Ql \&| .
|
|
The standard output of all but
|
|
the last command is connected to the standard input
|
|
of the next command.
|
|
The standard output of the last
|
|
command is inherited from the shell, as usual.
|
|
.Pp
|
|
The format for a pipeline is:
|
|
.Pp
|
|
.D1 Oo Li \&! Oc Ar command1 Op Li \&| Ar command2 ...
|
|
.Pp
|
|
The standard output of
|
|
.Ar command1
|
|
is connected to the standard input of
|
|
.Ar command2 .
|
|
The standard input, standard output, or
|
|
both of a command is considered to be assigned by the
|
|
pipeline before any redirection specified by redirection
|
|
operators that are part of the command.
|
|
.Pp
|
|
Note that unlike some other shells,
|
|
.Nm
|
|
executes each process in a pipeline with more than one command
|
|
in a subshell environment and as a child of the
|
|
.Nm
|
|
process.
|
|
.Pp
|
|
If the pipeline is not in the background (discussed later),
|
|
the shell waits for all commands to complete.
|
|
.Pp
|
|
If the keyword
|
|
.Ic !\&
|
|
does not precede the pipeline, the
|
|
exit status is the exit status of the last command specified
|
|
in the pipeline.
|
|
Otherwise, the exit status is the logical
|
|
NOT of the exit status of the last command.
|
|
That is, if
|
|
the last command returns zero, the exit status is 1; if
|
|
the last command returns greater than zero, the exit status
|
|
is zero.
|
|
.Pp
|
|
Because pipeline assignment of standard input or standard
|
|
output or both takes place before redirection, it can be
|
|
modified by redirection.
|
|
For example:
|
|
.Pp
|
|
.Dl "command1 2>&1 | command2"
|
|
.Pp
|
|
sends both the standard output and standard error of
|
|
.Ar command1
|
|
to the standard input of
|
|
.Ar command2 .
|
|
.Pp
|
|
A
|
|
.Ql \&;
|
|
or newline terminator causes the preceding
|
|
AND-OR-list
|
|
(described below in the section called
|
|
.Sx Short-Circuit List Operators )
|
|
to be executed sequentially;
|
|
an
|
|
.Ql &
|
|
causes asynchronous execution of the preceding AND-OR-list.
|
|
.Ss Background Commands (&)
|
|
If a command is terminated by the control operator ampersand
|
|
.Pq Ql & ,
|
|
the shell executes the command in a subshell environment (see
|
|
.Sx Grouping Commands Together
|
|
below) and asynchronously;
|
|
the shell does not wait for the command to finish
|
|
before executing the next command.
|
|
.Pp
|
|
The format for running a command in background is:
|
|
.Pp
|
|
.D1 Ar command1 Li & Op Ar command2 Li & Ar ...
|
|
.Pp
|
|
If the shell is not interactive, the standard input of an
|
|
asynchronous command is set to
|
|
.Pa /dev/null .
|
|
.Pp
|
|
The exit status is zero.
|
|
.Ss Lists (Generally Speaking)
|
|
A list is a sequence of zero or more commands separated by
|
|
newlines, semicolons, or ampersands,
|
|
and optionally terminated by one of these three characters.
|
|
The commands in a
|
|
list are executed in the order they are written.
|
|
If command is followed by an ampersand, the shell starts the
|
|
command and immediately proceeds onto the next command;
|
|
otherwise it waits for the command to terminate before
|
|
proceeding to the next one.
|
|
.Ss Short-Circuit List Operators
|
|
.Dq Li &&
|
|
and
|
|
.Dq Li ||
|
|
are AND-OR list operators.
|
|
.Dq Li &&
|
|
executes the first command, and then executes the second command
|
|
if the exit status of the first command is zero.
|
|
.Dq Li ||
|
|
is similar, but executes the second command if the exit
|
|
status of the first command is nonzero.
|
|
.Dq Li &&
|
|
and
|
|
.Dq Li ||
|
|
both have the same priority.
|
|
.Ss Flow-Control Constructs (if, while, for, case)
|
|
The syntax of the
|
|
.Ic if
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic if Ar list
|
|
.Ic then Ar list
|
|
.Oo Ic elif Ar list
|
|
.Ic then Ar list Oc Ar ...
|
|
.Op Ic else Ar list
|
|
.Ic fi
|
|
.Ed
|
|
.Pp
|
|
The exit status is that of selected
|
|
.Ic then
|
|
or
|
|
.Ic else
|
|
list,
|
|
or zero if no list was selected.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic while
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic while Ar list
|
|
.Ic do Ar list
|
|
.Ic done
|
|
.Ed
|
|
.Pp
|
|
The two lists are executed repeatedly while the exit status of the
|
|
first list is zero.
|
|
The
|
|
.Ic until
|
|
command is similar, but has the word
|
|
.Ic until
|
|
in place of
|
|
.Ic while ,
|
|
which causes it to
|
|
repeat until the exit status of the first list is zero.
|
|
.Pp
|
|
The exit status is that of the last execution of the second list,
|
|
or zero if it was never executed.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic for
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic for Ar variable Op Ic in Ar word ...
|
|
.Ic do Ar list
|
|
.Ic done
|
|
.Ed
|
|
.Pp
|
|
If
|
|
.Ic in
|
|
and the following words are omitted,
|
|
.Ic in Li \&"$@\&"
|
|
is used instead.
|
|
The words are expanded, and then the list is executed
|
|
repeatedly with the variable set to each word in turn.
|
|
The
|
|
.Ic do
|
|
and
|
|
.Ic done
|
|
commands may be replaced with
|
|
.Ql {
|
|
and
|
|
.Ql } .
|
|
.Pp
|
|
The syntax of the
|
|
.Ic break
|
|
and
|
|
.Ic continue
|
|
commands is:
|
|
.D1 Ic break Op Ar num
|
|
.D1 Ic continue Op Ar num
|
|
.Pp
|
|
The
|
|
.Ic break
|
|
command terminates the
|
|
.Ar num
|
|
innermost
|
|
.Ic for
|
|
or
|
|
.Ic while
|
|
loops.
|
|
The
|
|
.Ic continue
|
|
command continues with the next iteration of the innermost loop.
|
|
These are implemented as special built-in commands.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic case
|
|
command is:
|
|
.Bd -unfilled -offset indent -compact
|
|
.Ic case Ar word Ic in
|
|
.Ar pattern Ns Li ) Ar list Li ;;
|
|
.Ar ...
|
|
.Ic esac
|
|
.Ed
|
|
.Pp
|
|
The pattern can actually be one or more patterns
|
|
(see
|
|
.Sx Shell Patterns
|
|
described later),
|
|
separated by
|
|
.Ql \&|
|
|
characters.
|
|
Tilde expansion, parameter expansion, command substitution,
|
|
arithmetic expansion and quote removal are applied to the word.
|
|
Then, each pattern is expanded in turn using tilde expansion,
|
|
parameter expansion, command substitution and arithmetic expansion and
|
|
the expanded form of the word is checked against it.
|
|
If a match is found, the corresponding list is executed.
|
|
If the selected list is terminated by the control operator
|
|
.Ql ;&
|
|
instead of
|
|
.Ql ;; ,
|
|
execution continues with the next list,
|
|
continuing until a list terminated with
|
|
.Ql ;;
|
|
or the end of the
|
|
.Ic case
|
|
command.
|
|
.Ss Grouping Commands Together
|
|
Commands may be grouped by writing either
|
|
.Pp
|
|
.D1 Li \&( Ns Ar list Ns Li \%)
|
|
.Pp
|
|
or
|
|
.Pp
|
|
.D1 Li { Ar list Ns Li \&; }
|
|
.Pp
|
|
The first form executes the commands in a subshell environment.
|
|
A subshell environment has its own copy of:
|
|
.Bl -enum
|
|
.It
|
|
The current working directory as set by
|
|
.Ic cd .
|
|
.It
|
|
The file creation mask as set by
|
|
.Ic umask .
|
|
.It
|
|
Resource limits as set by
|
|
.Ic ulimit .
|
|
.It
|
|
References to open files.
|
|
.It
|
|
Traps as set by
|
|
.Ic trap .
|
|
.It
|
|
Known jobs.
|
|
.It
|
|
Positional parameters and variables.
|
|
.It
|
|
Shell options.
|
|
.It
|
|
Shell functions.
|
|
.It
|
|
Shell aliases.
|
|
.El
|
|
.Pp
|
|
These are copied from the parent shell environment,
|
|
except that trapped (but not ignored) signals are reset to the default action
|
|
and known jobs are cleared.
|
|
Any changes do not affect the parent shell environment.
|
|
.Pp
|
|
A subshell environment may be implemented as a child process or differently.
|
|
If job control is enabled in an interactive shell,
|
|
commands grouped in parentheses can be suspended and continued as a unit.
|
|
.Pp
|
|
For compatibility with other shells,
|
|
two open parentheses in sequence should be separated by whitespace.
|
|
.Pp
|
|
The second form never forks another shell,
|
|
so it is slightly more efficient.
|
|
Grouping commands together this way allows the user to
|
|
redirect their output as though they were one program:
|
|
.Bd -literal -offset indent
|
|
{ echo -n "hello"; echo " world"; } > greeting
|
|
.Ed
|
|
.Ss Functions
|
|
The syntax of a function definition is
|
|
.Pp
|
|
.D1 Ar name Li \&( \&) Ar command
|
|
.Pp
|
|
A function definition is an executable statement; when
|
|
executed it installs a function named
|
|
.Ar name
|
|
and returns an
|
|
exit status of zero.
|
|
The
|
|
.Ar command
|
|
is normally a list
|
|
enclosed between
|
|
.Ql {
|
|
and
|
|
.Ql } .
|
|
.Pp
|
|
Variables may be declared to be local to a function by
|
|
using the
|
|
.Ic local
|
|
command.
|
|
This should appear as the first statement of a function,
|
|
and the syntax is:
|
|
.Pp
|
|
.D1 Ic local Oo Ar variable ... Oc Op Fl
|
|
.Pp
|
|
The
|
|
.Ic local
|
|
command is implemented as a built-in command.
|
|
The exit status is zero
|
|
unless the command is not in a function or a variable name is invalid.
|
|
.Pp
|
|
When a variable is made local, it inherits the initial
|
|
value and exported and readonly flags from the variable
|
|
with the same name in the surrounding scope, if there is
|
|
one.
|
|
Otherwise, the variable is initially unset.
|
|
The shell
|
|
uses dynamic scoping, so that if the variable
|
|
.Va x
|
|
is made local to function
|
|
.Em f ,
|
|
which then calls function
|
|
.Em g ,
|
|
references to the variable
|
|
.Va x
|
|
made inside
|
|
.Em g
|
|
will refer to the variable
|
|
.Va x
|
|
declared inside
|
|
.Em f ,
|
|
not to the global variable named
|
|
.Va x .
|
|
.Pp
|
|
The only special parameter that can be made local is
|
|
.Ql - .
|
|
Making
|
|
.Ql -
|
|
local causes any shell options
|
|
(including those that only have long names)
|
|
that are
|
|
changed via the
|
|
.Ic set
|
|
command inside the function to be
|
|
restored to their original values when the function
|
|
returns.
|
|
.Pp
|
|
The syntax of the
|
|
.Ic return
|
|
command is
|
|
.Pp
|
|
.D1 Ic return Op Ar exitstatus
|
|
.Pp
|
|
It terminates the current executional scope, returning from the closest
|
|
nested function or sourced script;
|
|
if no function or sourced script is being executed,
|
|
it exits the shell instance.
|
|
The
|
|
.Ic return
|
|
command is implemented as a special built-in command.
|
|
.Ss Variables and Parameters
|
|
The shell maintains a set of parameters.
|
|
A parameter
|
|
denoted by a name
|
|
(consisting solely
|
|
of alphabetics, numerics, and underscores,
|
|
and starting with an alphabetic or an underscore)
|
|
is called a variable.
|
|
When starting up,
|
|
the shell turns all environment variables with valid names into shell
|
|
variables.
|
|
New variables can be set using the form
|
|
.Pp
|
|
.D1 Ar name Ns = Ns Ar value
|
|
.Pp
|
|
A parameter can also be denoted by a number
|
|
or a special character as explained below.
|
|
.Pp
|
|
Assignments are expanded differently from other words:
|
|
tilde expansion is also performed after the equals sign and after any colon
|
|
and usernames are also terminated by colons,
|
|
and field splitting and pathname expansion are not performed.
|
|
.Pp
|
|
This special expansion applies not only to assignments that form a simple
|
|
command by themselves or precede a command word,
|
|
but also to words passed to the
|
|
.Ic export ,
|
|
.Ic local
|
|
or
|
|
.Ic readonly
|
|
built-in commands that have this form.
|
|
For this, the builtin's name must be literal
|
|
(not the result of an expansion)
|
|
and may optionally be preceded by one or more literal instances of
|
|
.Ic command
|
|
without options.
|
|
.Ss Positional Parameters
|
|
A positional parameter is a parameter denoted by a number greater than zero.
|
|
The shell sets these initially to the values of its command line
|
|
arguments that follow the name of the shell script.
|
|
The
|
|
.Ic set
|
|
built-in command can also be used to set or reset them.
|
|
.Ss Special Parameters
|
|
Special parameters are parameters denoted by a single special character
|
|
or the digit zero.
|
|
They are shown in the following list, exactly as they would appear in input
|
|
typed by the user or in the source of a shell script.
|
|
.Bl -hang
|
|
.It Li $*
|
|
Expands to the positional parameters, starting from one.
|
|
When
|
|
the expansion occurs within a double-quoted string
|
|
it expands to a single field with the value of each parameter
|
|
separated by the first character of the
|
|
.Va IFS
|
|
variable,
|
|
or by a space if
|
|
.Va IFS
|
|
is unset.
|
|
.It Li $@
|
|
Expands to the positional parameters, starting from one.
|
|
When
|
|
the expansion occurs within double-quotes, each positional
|
|
parameter expands as a separate argument.
|
|
If there are no positional parameters, the
|
|
expansion of
|
|
.Li @
|
|
generates zero arguments, even when
|
|
.Li @
|
|
is double-quoted.
|
|
What this basically means, for example, is
|
|
if
|
|
.Li $1
|
|
is
|
|
.Dq Li abc
|
|
and
|
|
.Li $2
|
|
is
|
|
.Dq Li "def ghi" ,
|
|
then
|
|
.Li \&"$@\&"
|
|
expands to
|
|
the two arguments:
|
|
.Bd -literal -offset indent
|
|
"abc" "def ghi"
|
|
.Ed
|
|
.It Li $#
|
|
Expands to the number of positional parameters.
|
|
.It Li $?
|
|
Expands to the exit status of the most recent pipeline.
|
|
.It Li $-
|
|
(hyphen) Expands to the current option flags (the single-letter
|
|
option names concatenated into a string) as specified on
|
|
invocation, by the
|
|
.Ic set
|
|
built-in command, or implicitly
|
|
by the shell.
|
|
.It Li $$
|
|
Expands to the process ID of the invoked shell.
|
|
A subshell
|
|
retains the same value of
|
|
.Va $
|
|
as its parent.
|
|
.It Li $!
|
|
Expands to the process ID of the most recent background
|
|
command executed from the current shell.
|
|
For a
|
|
pipeline, the process ID is that of the last command in the
|
|
pipeline.
|
|
If this parameter is referenced, the shell will remember
|
|
the process ID and its exit status until the
|
|
.Ic wait
|
|
built-in command reports completion of the process.
|
|
.It Li $0
|
|
(zero) Expands to the name of the shell script if passed on the command line,
|
|
the
|
|
.Ar name
|
|
operand if given (with
|
|
.Fl c )
|
|
or otherwise argument 0 passed to the shell.
|
|
.El
|
|
.Ss Special Variables
|
|
The following variables are set by the shell or
|
|
have special meaning to it:
|
|
.Bl -tag -width ".Va HISTSIZE"
|
|
.It Va CDPATH
|
|
The search path used with the
|
|
.Ic cd
|
|
built-in.
|
|
.It Va EDITOR
|
|
The fallback editor used with the
|
|
.Ic fc
|
|
built-in.
|
|
If not set, the default editor is
|
|
.Xr ed 1 .
|
|
.It Va FCEDIT
|
|
The default editor used with the
|
|
.Ic fc
|
|
built-in.
|
|
.It Va HISTSIZE
|
|
The number of previous commands that are accessible.
|
|
.It Va HOME
|
|
The user's home directory,
|
|
used in tilde expansion and as a default directory for the
|
|
.Ic cd
|
|
built-in.
|
|
.It Va IFS
|
|
Input Field Separators.
|
|
The default value is
|
|
.Aq space ,
|
|
.Aq tab ,
|
|
and
|
|
.Aq newline
|
|
in that order.
|
|
This default also applies if
|
|
.Va IFS
|
|
is unset, but not if it is set to the empty string.
|
|
See the
|
|
.Sx White Space Splitting
|
|
section for more details.
|
|
.It Va LINENO
|
|
The current line number in the script or function.
|
|
.It Va MAIL
|
|
The name of a mail file, that will be checked for the arrival of new
|
|
mail.
|
|
Overridden by
|
|
.Va MAILPATH .
|
|
.It Va MAILPATH
|
|
A colon
|
|
.Pq Ql \&:
|
|
separated list of file names, for the shell to check for incoming
|
|
mail.
|
|
This variable overrides the
|
|
.Va MAIL
|
|
setting.
|
|
There is a maximum of 10 mailboxes that can be monitored at once.
|
|
.It Va OPTIND
|
|
The index of the next argument to be processed by
|
|
.Ic getopts .
|
|
This is initialized to 1 at startup.
|
|
.It Va PATH
|
|
The default search path for executables.
|
|
See the
|
|
.Sx Path Search
|
|
section for details.
|
|
.It Va PPID
|
|
The parent process ID of the invoked shell.
|
|
This is set at startup
|
|
unless this variable is in the environment.
|
|
A later change of parent process ID is not reflected.
|
|
A subshell retains the same value of
|
|
.Va PPID .
|
|
.It Va PS1
|
|
The primary prompt string, which defaults to
|
|
.Dq Li "$ " ,
|
|
unless you are the superuser, in which case it defaults to
|
|
.Dq Li "# " .
|
|
.Va PS1
|
|
may include any of the following formatting sequences,
|
|
which are replaced by the given information:
|
|
.Bl -tag -width indent
|
|
.It Li \eH
|
|
The local hostname.
|
|
.It Li \eh
|
|
The fully-qualified hostname.
|
|
.It Li \eW
|
|
The final component of the current working directory.
|
|
.It Li \ew
|
|
The entire path of the current working directory.
|
|
.It Li \e$
|
|
Superuser status.
|
|
.Dq Li "$ "
|
|
for normal users and
|
|
.Dq Li "# "
|
|
for superusers.
|
|
.It Li \e\e
|
|
A literal backslash.
|
|
.El
|
|
.It Va PS2
|
|
The secondary prompt string, which defaults to
|
|
.Dq Li "> " .
|
|
.Va PS2
|
|
may include any of the formatting sequences from
|
|
.Va PS1 .
|
|
.It Va PS4
|
|
The prefix for the trace output (if
|
|
.Fl x
|
|
is active).
|
|
The default is
|
|
.Dq Li "+ " .
|
|
.El
|
|
.Ss Word Expansions
|
|
This clause describes the various expansions that are
|
|
performed on words.
|
|
Not all expansions are performed on
|
|
every word, as explained later.
|
|
.Pp
|
|
Tilde expansions, parameter expansions, command substitutions,
|
|
arithmetic expansions, and quote removals that occur within
|
|
a single word expand to a single field.
|
|
It is only field
|
|
splitting or pathname expansion that can create multiple
|
|
fields from a single word.
|
|
The single exception to this rule is
|
|
the expansion of the special parameter
|
|
.Va @
|
|
within double-quotes,
|
|
as was described above.
|
|
.Pp
|
|
The order of word expansion is:
|
|
.Bl -enum
|
|
.It
|
|
Tilde Expansion, Parameter Expansion, Command Substitution,
|
|
Arithmetic Expansion (these all occur at the same time).
|
|
.It
|
|
Field Splitting is performed on fields generated by step (1)
|
|
unless the
|
|
.Va IFS
|
|
variable is null.
|
|
.It
|
|
Pathname Expansion (unless the
|
|
.Fl f
|
|
option is in effect).
|
|
.It
|
|
Quote Removal.
|
|
.El
|
|
.Pp
|
|
The
|
|
.Ql $
|
|
character is used to introduce parameter expansion, command
|
|
substitution, or arithmetic expansion.
|
|
.Ss Tilde Expansion (substituting a user's home directory)
|
|
A word beginning with an unquoted tilde character
|
|
.Pq Ql ~
|
|
is
|
|
subjected to tilde expansion.
|
|
All the characters up to a slash
|
|
.Pq Ql /
|
|
or the end of the word are treated as a username
|
|
and are replaced with the user's home directory.
|
|
If the
|
|
username is missing (as in
|
|
.Pa ~/foobar ) ,
|
|
the tilde is replaced with the value of the
|
|
.Va HOME
|
|
variable (the current user's home directory).
|
|
.Ss Parameter Expansion
|
|
The format for parameter expansion is as follows:
|
|
.Pp
|
|
.D1 Li ${ Ns Ar expression Ns Li }
|
|
.Pp
|
|
where
|
|
.Ar expression
|
|
consists of all characters until the matching
|
|
.Ql } .
|
|
Any
|
|
.Ql }
|
|
escaped by a backslash or within a single-quoted or double-quoted
|
|
string, and characters in
|
|
embedded arithmetic expansions, command substitutions, and variable
|
|
expansions, are not examined in determining the matching
|
|
.Ql } .
|
|
If the variants with
|
|
.Ql + ,
|
|
.Ql - ,
|
|
.Ql =
|
|
or
|
|
.Ql ?\&
|
|
occur within a double-quoted string,
|
|
as an extension there may be unquoted parts
|
|
(via double-quotes inside the expansion);
|
|
.Ql }
|
|
within such parts are also not examined in determining the matching
|
|
.Ql } .
|
|
.Pp
|
|
The simplest form for parameter expansion is:
|
|
.Pp
|
|
.D1 Li ${ Ns Ar parameter Ns Li }
|
|
.Pp
|
|
The value, if any, of
|
|
.Ar parameter
|
|
is substituted.
|
|
.Pp
|
|
The parameter name or symbol can be enclosed in braces, which are
|
|
optional except for positional parameters with more than one digit or
|
|
when parameter is followed by a character that could be interpreted as
|
|
part of the name.
|
|
If a parameter expansion occurs inside double-quotes:
|
|
.Bl -enum
|
|
.It
|
|
Field splitting is not performed on the results of the
|
|
expansion, with the exception of the special parameter
|
|
.Va @ .
|
|
.It
|
|
Pathname expansion is not performed on the results of the
|
|
expansion.
|
|
.El
|
|
.Pp
|
|
In addition, a parameter expansion can be modified by using one of the
|
|
following formats.
|
|
.Bl -tag -width indent
|
|
.It Li ${ Ns Ar parameter Ns Li :- Ns Ar word Ns Li }
|
|
Use Default Values.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, the expansion of
|
|
.Ar word
|
|
is substituted; otherwise, the value of
|
|
.Ar parameter
|
|
is substituted.
|
|
.It Li ${ Ns Ar parameter Ns Li := Ns Ar word Ns Li }
|
|
Assign Default Values.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, the expansion of
|
|
.Ar word
|
|
is assigned to
|
|
.Ar parameter .
|
|
In all cases, the
|
|
final value of
|
|
.Ar parameter
|
|
is substituted.
|
|
Quoting inside
|
|
.Ar word
|
|
does not prevent field splitting or pathname expansion.
|
|
Only variables, not positional
|
|
parameters or special parameters, can be
|
|
assigned in this way.
|
|
.It Li ${ Ns Ar parameter Ns Li :? Ns Oo Ar word Oc Ns Li }
|
|
Indicate Error if Null or Unset.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, the expansion of
|
|
.Ar word
|
|
(or a message indicating it is unset if
|
|
.Ar word
|
|
is omitted) is written to standard
|
|
error and the shell exits with a nonzero
|
|
exit status.
|
|
Otherwise, the value of
|
|
.Ar parameter
|
|
is substituted.
|
|
An
|
|
interactive shell need not exit.
|
|
.It Li ${ Ns Ar parameter Ns Li :+ Ns Ar word Ns Li }
|
|
Use Alternate Value.
|
|
If
|
|
.Ar parameter
|
|
is unset or null, null is substituted;
|
|
otherwise, the expansion of
|
|
.Ar word
|
|
is substituted.
|
|
.El
|
|
.Pp
|
|
In the parameter expansions shown previously, use of the colon in the
|
|
format results in a test for a parameter that is unset or null; omission
|
|
of the colon results in a test for a parameter that is only unset.
|
|
.Pp
|
|
The
|
|
.Ar word
|
|
inherits the type of quoting
|
|
(unquoted, double-quoted or here-document)
|
|
from the surroundings,
|
|
with the exception that a backslash that quotes a closing brace is removed
|
|
during quote removal.
|
|
.Bl -tag -width indent
|
|
.It Li ${# Ns Ar parameter Ns Li }
|
|
String Length.
|
|
The length in characters of
|
|
the value of
|
|
.Ar parameter .
|
|
.El
|
|
.Pp
|
|
The following four varieties of parameter expansion provide for substring
|
|
processing.
|
|
In each case, pattern matching notation
|
|
(see
|
|
.Sx Shell Patterns ) ,
|
|
rather than regular expression notation,
|
|
is used to evaluate the patterns.
|
|
If parameter is one of the special parameters
|
|
.Va *
|
|
or
|
|
.Va @ ,
|
|
the result of the expansion is unspecified.
|
|
Enclosing the full parameter expansion string in double-quotes does not
|
|
cause the following four varieties of pattern characters to be quoted,
|
|
whereas quoting characters within the braces has this effect.
|
|
.Bl -tag -width indent
|
|
.It Li ${ Ns Ar parameter Ns Li % Ns Ar word Ns Li }
|
|
Remove Smallest Suffix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar parameter ,
|
|
with the smallest portion of the
|
|
suffix matched by the pattern deleted.
|
|
.It Li ${ Ns Ar parameter Ns Li %% Ns Ar word Ns Li }
|
|
Remove Largest Suffix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar parameter ,
|
|
with the largest portion of the
|
|
suffix matched by the pattern deleted.
|
|
.It Li ${ Ns Ar parameter Ns Li # Ns Ar word Ns Li }
|
|
Remove Smallest Prefix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar parameter ,
|
|
with the smallest portion of the
|
|
prefix matched by the pattern deleted.
|
|
.It Li ${ Ns Ar parameter Ns Li ## Ns Ar word Ns Li }
|
|
Remove Largest Prefix Pattern.
|
|
The
|
|
.Ar word
|
|
is expanded to produce a pattern.
|
|
The
|
|
parameter expansion then results in
|
|
.Ar parameter ,
|
|
with the largest portion of the
|
|
prefix matched by the pattern deleted.
|
|
.El
|
|
.Ss Command Substitution
|
|
Command substitution allows the output of a command to be substituted in
|
|
place of the command name itself.
|
|
Command substitution occurs when
|
|
the command is enclosed as follows:
|
|
.Pp
|
|
.D1 Li $( Ns Ar command Ns Li )\&
|
|
.Pp
|
|
or the backquoted version:
|
|
.Pp
|
|
.D1 Li ` Ns Ar command Ns Li `
|
|
.Pp
|
|
The shell expands the command substitution by executing command
|
|
and replacing the command substitution
|
|
with the standard output of the command,
|
|
removing sequences of one or more newlines at the end of the substitution.
|
|
Embedded newlines before the end of the output are not removed;
|
|
however, during field splitting, they may be translated into spaces
|
|
depending on the value of
|
|
.Va IFS
|
|
and the quoting that is in effect.
|
|
The command is executed in a subshell environment,
|
|
except that the built-in commands
|
|
.Ic jobid ,
|
|
.Ic jobs ,
|
|
and
|
|
.Ic trap
|
|
return information about the parent shell environment
|
|
and
|
|
.Ic times
|
|
returns information about the same process
|
|
if they are the only command in a command substitution.
|
|
.Pp
|
|
If a command substitution of the
|
|
.Li $(
|
|
form begins with a subshell,
|
|
the
|
|
.Li $(
|
|
and
|
|
.Li (\&
|
|
must be separated by whitespace
|
|
to avoid ambiguity with arithmetic expansion.
|
|
.Ss Arithmetic Expansion
|
|
Arithmetic expansion provides a mechanism for evaluating an arithmetic
|
|
expression and substituting its value.
|
|
The format for arithmetic expansion is as follows:
|
|
.Pp
|
|
.D1 Li $(( Ns Ar expression Ns Li ))
|
|
.Pp
|
|
The
|
|
.Ar expression
|
|
is treated as if it were in double-quotes, except
|
|
that a double-quote inside the expression is not treated specially.
|
|
The
|
|
shell expands all tokens in the
|
|
.Ar expression
|
|
for parameter expansion,
|
|
command substitution,
|
|
arithmetic expansion
|
|
and quote removal.
|
|
.Pp
|
|
The allowed expressions are a subset of C expressions,
|
|
summarized below.
|
|
.Bl -tag -width "Variables" -offset indent
|
|
.It Values
|
|
All values are of type
|
|
.Ft intmax_t .
|
|
.It Constants
|
|
Decimal, octal (starting with
|
|
.Li 0 )
|
|
and hexadecimal (starting with
|
|
.Li 0x )
|
|
integer constants.
|
|
.It Variables
|
|
Shell variables can be read and written
|
|
and contain integer constants.
|
|
.It Unary operators
|
|
.Li "! ~ + -"
|
|
.It Binary operators
|
|
.Li "* / % + - << >> < <= > >= == != & ^ | && ||"
|
|
.It Assignment operators
|
|
.Li "= += -= *= /= %= <<= >>= &= ^= |="
|
|
.It Conditional operator
|
|
.Li "? :"
|
|
.El
|
|
.Pp
|
|
The result of the expression is substituted in decimal.
|
|
.Ss White Space Splitting (Field Splitting)
|
|
In certain contexts,
|
|
after parameter expansion, command substitution, and
|
|
arithmetic expansion the shell scans the results of
|
|
expansions and substitutions that did not occur in double-quotes for
|
|
field splitting and multiple fields can result.
|
|
.Pp
|
|
Characters in
|
|
.Va IFS
|
|
that are whitespace
|
|
.Po
|
|
.Aq space ,
|
|
.Aq tab ,
|
|
and
|
|
.Aq newline
|
|
.Pc
|
|
are treated differently from other characters in
|
|
.Va IFS .
|
|
.Pp
|
|
Whitespace in
|
|
.Va IFS
|
|
at the beginning or end of a word is discarded.
|
|
.Pp
|
|
Subsequently, a field is delimited by either
|
|
.Bl -enum
|
|
.It
|
|
a non-whitespace character in
|
|
.Va IFS
|
|
with any whitespace in
|
|
.Va IFS
|
|
surrounding it, or
|
|
.It
|
|
one or more whitespace characters in
|
|
.Va IFS .
|
|
.El
|
|
.Pp
|
|
If a word ends with a non-whitespace character in
|
|
.Va IFS ,
|
|
there is no empty field after this character.
|
|
.Pp
|
|
If no field is delimited, the word is discarded.
|
|
In particular, if a word consists solely of an unquoted substitution
|
|
and the result of the substitution is null,
|
|
it is removed by field splitting even if
|
|
.Va IFS
|
|
is null.
|
|
.Ss Pathname Expansion (File Name Generation)
|
|
Unless the
|
|
.Fl f
|
|
option is set,
|
|
file name generation is performed
|
|
after word splitting is complete.
|
|
Each word is
|
|
viewed as a series of patterns, separated by slashes.
|
|
The
|
|
process of expansion replaces the word with the names of
|
|
all existing files whose names can be formed by replacing
|
|
each pattern with a string that matches the specified pattern.
|
|
There are two restrictions on this: first, a pattern cannot match
|
|
a string containing a slash, and second,
|
|
a pattern cannot match a string starting with a period
|
|
unless the first character of the pattern is a period.
|
|
The next section describes the patterns used for
|
|
Pathname Expansion,
|
|
the four varieties of parameter expansion for substring processing and the
|
|
.Ic case
|
|
command.
|
|
.Ss Shell Patterns
|
|
A pattern consists of normal characters, which match themselves,
|
|
and meta-characters.
|
|
The meta-characters are
|
|
.Ql * ,
|
|
.Ql \&? ,
|
|
and
|
|
.Ql \&[ .
|
|
These characters lose their special meanings if they are quoted.
|
|
When command or variable substitution is performed and the dollar sign
|
|
or back quotes are not double-quoted, the value of the
|
|
variable or the output of the command is scanned for these
|
|
characters and they are turned into meta-characters.
|
|
.Pp
|
|
An asterisk
|
|
.Pq Ql *
|
|
matches any string of characters.
|
|
A question mark
|
|
.Pq Ql \&?
|
|
matches any single character.
|
|
A left bracket
|
|
.Pq Ql \&[
|
|
introduces a character class.
|
|
The end of the character class is indicated by a
|
|
.Ql \&] ;
|
|
if the
|
|
.Ql \&]
|
|
is missing then the
|
|
.Ql \&[
|
|
matches a
|
|
.Ql \&[
|
|
rather than introducing a character class.
|
|
A character class matches any of the characters between the square brackets.
|
|
A locale-dependent range of characters may be specified using a minus sign.
|
|
A named class of characters (see
|
|
.Xr wctype 3 )
|
|
may be specified by surrounding the name with
|
|
.Ql \&[:
|
|
and
|
|
.Ql :\&] .
|
|
For example,
|
|
.Ql \&[\&[:alpha:\&]\&]
|
|
is a shell pattern that matches a single letter.
|
|
The character class may be complemented by making an exclamation point
|
|
.Pq Ql !\&
|
|
the first character of the character class.
|
|
A caret
|
|
.Pq Ql ^
|
|
has the same effect but is non-standard.
|
|
.Pp
|
|
To include a
|
|
.Ql \&]
|
|
in a character class, make it the first character listed
|
|
(after the
|
|
.Ql \&!
|
|
or
|
|
.Ql ^ ,
|
|
if any).
|
|
To include a
|
|
.Ql - ,
|
|
make it the first or last character listed.
|
|
.Ss Built-in Commands
|
|
This section lists the built-in commands.
|
|
.Bl -tag -width indent
|
|
.It Ic \&:
|
|
A null command that returns a 0 (true) exit value.
|
|
.It Ic \&. Ar file
|
|
The commands in the specified file are read and executed by the shell.
|
|
The
|
|
.Ic return
|
|
command may be used to return to the
|
|
.Ic \&.
|
|
command's caller.
|
|
If
|
|
.Ar file
|
|
contains any
|
|
.Ql /
|
|
characters, it is used as is.
|
|
Otherwise, the shell searches the
|
|
.Va PATH
|
|
for the file.
|
|
If it is not found in the
|
|
.Va PATH ,
|
|
it is sought in the current working directory.
|
|
.It Ic \&[
|
|
A built-in equivalent of
|
|
.Xr test 1 .
|
|
.It Ic alias Oo Ar name Ns Oo = Ns Ar string Oc ... Oc
|
|
If
|
|
.Ar name Ns = Ns Ar string
|
|
is specified, the shell defines the alias
|
|
.Ar name
|
|
with value
|
|
.Ar string .
|
|
If just
|
|
.Ar name
|
|
is specified, the value of the alias
|
|
.Ar name
|
|
is printed.
|
|
With no arguments, the
|
|
.Ic alias
|
|
built-in command prints the names and values of all defined aliases
|
|
(see
|
|
.Ic unalias ) .
|
|
Alias values are written with appropriate quoting so that they are
|
|
suitable for re-input to the shell.
|
|
Also see the
|
|
.Sx Aliases
|
|
subsection.
|
|
.It Ic bg Op Ar job ...
|
|
Continue the specified jobs
|
|
(or the current job if no jobs are given)
|
|
in the background.
|
|
.It Ic bind Oo Fl aeklrsv Oc Oo Ar key Oo Ar command Oc Oc
|
|
List or alter key bindings for the line editor.
|
|
This command is documented in
|
|
.Xr editrc 5 .
|
|
.It Ic break Op Ar num
|
|
See the
|
|
.Sx Flow-Control Constructs
|
|
subsection.
|
|
.It Ic builtin Ar cmd Op Ar arg ...
|
|
Execute the specified built-in command,
|
|
.Ar cmd .
|
|
This is useful when the user wishes to override a shell function
|
|
with the same name as a built-in command.
|
|
.It Ic cd Oo Fl L | P Oc Oo Fl e Oc Op Ar directory
|
|
Switch to the specified
|
|
.Ar directory ,
|
|
or to the directory specified in the
|
|
.Va HOME
|
|
environment variable if no
|
|
.Ar directory
|
|
is specified.
|
|
If
|
|
.Ar directory
|
|
does not begin with
|
|
.Pa / , \&. ,
|
|
or
|
|
.Pa .. ,
|
|
then the directories listed in the
|
|
.Va CDPATH
|
|
variable will be
|
|
searched for the specified
|
|
.Ar directory .
|
|
If
|
|
.Va CDPATH
|
|
is unset, the current directory is searched.
|
|
The format of
|
|
.Va CDPATH
|
|
is the same as that of
|
|
.Va PATH .
|
|
In an interactive shell,
|
|
the
|
|
.Ic cd
|
|
command will print out the name of the directory
|
|
that it actually switched to
|
|
if this is different from the name that the user gave.
|
|
These may be different either because the
|
|
.Va CDPATH
|
|
mechanism was used or because a symbolic link was crossed.
|
|
.Pp
|
|
If the
|
|
.Fl P
|
|
option is specified,
|
|
.Pa ..
|
|
is handled physically and symbolic links are resolved before
|
|
.Pa ..
|
|
components are processed.
|
|
If the
|
|
.Fl L
|
|
option is specified,
|
|
.Pa ..
|
|
is handled logically.
|
|
This is the default.
|
|
.Pp
|
|
The
|
|
.Fl e
|
|
option causes
|
|
.Ic cd
|
|
to return exit status 1 if the full pathname of the new directory
|
|
cannot be determined reliably or at all.
|
|
Normally this is not considered an error,
|
|
although a warning is printed.
|
|
.It Ic chdir
|
|
A synonym for the
|
|
.Ic cd
|
|
built-in command.
|
|
.It Ic command Oo Fl p Oc Op Ar utility Op Ar argument ...
|
|
.It Ic command Oo Fl p Oc Fl v Ar utility
|
|
.It Ic command Oo Fl p Oc Fl V Ar utility
|
|
The first form of invocation executes the specified
|
|
.Ar utility ,
|
|
ignoring shell functions in the search.
|
|
If
|
|
.Ar utility
|
|
is a special builtin,
|
|
it is executed as if it were a regular builtin.
|
|
.Pp
|
|
If the
|
|
.Fl p
|
|
option is specified, the command search is performed using a
|
|
default value of
|
|
.Va PATH
|
|
that is guaranteed to find all of the standard utilities.
|
|
.Pp
|
|
If the
|
|
.Fl v
|
|
option is specified,
|
|
.Ar utility
|
|
is not executed but a description of its interpretation by the shell is
|
|
printed.
|
|
For ordinary commands the output is the path name; for shell built-in
|
|
commands, shell functions and keywords only the name is written.
|
|
Aliases are printed as
|
|
.Dq Ic alias Ar name Ns = Ns Ar value .
|
|
.Pp
|
|
The
|
|
.Fl V
|
|
option is identical to
|
|
.Fl v
|
|
except for the output.
|
|
It prints
|
|
.Dq Ar utility Ic is Ar description
|
|
where
|
|
.Ar description
|
|
is either
|
|
the path name to
|
|
.Ar utility ,
|
|
a special shell builtin,
|
|
a shell builtin,
|
|
a shell function,
|
|
a shell keyword
|
|
or
|
|
an alias for
|
|
.Ar value .
|
|
.It Ic continue Op Ar num
|
|
See the
|
|
.Sx Flow-Control Constructs
|
|
subsection.
|
|
.It Ic echo Oo Fl e | n Oc Op Ar string ...
|
|
Print a space-separated list of the arguments to the standard output
|
|
and append a newline character.
|
|
.Bl -tag -width indent
|
|
.It Fl n
|
|
Suppress the output of the trailing newline.
|
|
.It Fl e
|
|
Process C-style backslash escape sequences.
|
|
The
|
|
.Ic echo
|
|
command understands the following character escapes:
|
|
.Bl -tag -width indent
|
|
.It \ea
|
|
Alert (ring the terminal bell)
|
|
.It \eb
|
|
Backspace
|
|
.It \ec
|
|
Suppress the trailing newline (this has the side-effect of truncating the
|
|
line if it is not the last character)
|
|
.It \ee
|
|
The ESC character
|
|
.Tn ( ASCII
|
|
0x1b)
|
|
.It \ef
|
|
Formfeed
|
|
.It \en
|
|
Newline
|
|
.It \er
|
|
Carriage return
|
|
.It \et
|
|
Horizontal tab
|
|
.It \ev
|
|
Vertical tab
|
|
.It \e\e
|
|
Literal backslash
|
|
.It \e0nnn
|
|
(Zero) The character whose octal value is
|
|
.Ar nnn
|
|
.El
|
|
.Pp
|
|
If
|
|
.Ar string
|
|
is not enclosed in quotes then the backslash itself must be escaped
|
|
with a backslash to protect it from the shell.
|
|
For example
|
|
.Bd -literal -offset indent
|
|
$ echo -e "a\evb"
|
|
a
|
|
b
|
|
$ echo -e a\e\evb
|
|
a
|
|
b
|
|
$ echo -e "a\e\eb"
|
|
a\eb
|
|
$ echo -e a\e\e\e\eb
|
|
a\eb
|
|
.Ed
|
|
.El
|
|
.Pp
|
|
Only one of the
|
|
.Fl e
|
|
and
|
|
.Fl n
|
|
options may be specified.
|
|
.It Ic eval Ar string ...
|
|
Concatenate all the arguments with spaces.
|
|
Then re-parse and execute the command.
|
|
.It Ic exec Op Ar command Op arg ...
|
|
Unless
|
|
.Ar command
|
|
is omitted,
|
|
the shell process is replaced with the specified program
|
|
(which must be a real program, not a shell built-in command or function).
|
|
Any redirections on the
|
|
.Ic exec
|
|
command are marked as permanent,
|
|
so that they are not undone when the
|
|
.Ic exec
|
|
command finishes.
|
|
.It Ic exit Op Ar exitstatus
|
|
Terminate the shell process.
|
|
If
|
|
.Ar exitstatus
|
|
is given
|
|
it is used as the exit status of the shell.
|
|
Otherwise, if the shell is executing an
|
|
.Cm EXIT
|
|
trap, the exit status of the last command before the trap is used;
|
|
if the shell is executing a trap for a signal,
|
|
the shell exits by resending the signal to itself.
|
|
Otherwise, the exit status of the preceding command is used.
|
|
The exit status should be an integer between 0 and 255.
|
|
.It Ic export Ar name ...
|
|
.It Ic export Op Fl p
|
|
The specified names are exported so that they will
|
|
appear in the environment of subsequent commands.
|
|
The only way to un-export a variable is to
|
|
.Ic unset
|
|
it.
|
|
The shell allows the value of a variable to be set
|
|
at the same time as it is exported by writing
|
|
.Pp
|
|
.D1 Ic export Ar name Ns = Ns Ar value
|
|
.Pp
|
|
With no arguments the
|
|
.Ic export
|
|
command lists the names
|
|
of all exported variables.
|
|
If the
|
|
.Fl p
|
|
option is specified, the exported variables are printed as
|
|
.Dq Ic export Ar name Ns = Ns Ar value
|
|
lines, suitable for re-input to the shell.
|
|
.It Ic false
|
|
A null command that returns a non-zero (false) exit value.
|
|
.It Ic fc Oo Fl e Ar editor Oc Op Ar first Op Ar last
|
|
.It Ic fc Fl l Oo Fl nr Oc Op Ar first Op Ar last
|
|
.It Ic fc Fl s Oo Ar old Ns = Ns Ar new Oc Op Ar first
|
|
The
|
|
.Ic fc
|
|
built-in command lists, or edits and re-executes,
|
|
commands previously entered to an interactive shell.
|
|
.Bl -tag -width indent
|
|
.It Fl e Ar editor
|
|
Use the editor named by
|
|
.Ar editor
|
|
to edit the commands.
|
|
The
|
|
.Ar editor
|
|
string is a command name,
|
|
subject to search via the
|
|
.Va PATH
|
|
variable.
|
|
The value in the
|
|
.Va FCEDIT
|
|
variable is used as a default when
|
|
.Fl e
|
|
is not specified.
|
|
If
|
|
.Va FCEDIT
|
|
is null or unset, the value of the
|
|
.Va EDITOR
|
|
variable is used.
|
|
If
|
|
.Va EDITOR
|
|
is null or unset,
|
|
.Xr ed 1
|
|
is used as the editor.
|
|
.It Fl l No (ell)
|
|
List the commands rather than invoking
|
|
an editor on them.
|
|
The commands are written in the
|
|
sequence indicated by the
|
|
.Ar first
|
|
and
|
|
.Ar last
|
|
operands, as affected by
|
|
.Fl r ,
|
|
with each command preceded by the command number.
|
|
.It Fl n
|
|
Suppress command numbers when listing with
|
|
.Fl l .
|
|
.It Fl r
|
|
Reverse the order of the commands listed
|
|
(with
|
|
.Fl l )
|
|
or edited
|
|
(with neither
|
|
.Fl l
|
|
nor
|
|
.Fl s ) .
|
|
.It Fl s
|
|
Re-execute the command without invoking an editor.
|
|
.It Ar first
|
|
.It Ar last
|
|
Select the commands to list or edit.
|
|
The number of previous commands that can be accessed
|
|
are determined by the value of the
|
|
.Va HISTSIZE
|
|
variable.
|
|
The value of
|
|
.Ar first
|
|
or
|
|
.Ar last
|
|
or both are one of the following:
|
|
.Bl -tag -width indent
|
|
.It Oo Cm + Oc Ns Ar num
|
|
A positive number representing a command number;
|
|
command numbers can be displayed with the
|
|
.Fl l
|
|
option.
|
|
.It Fl Ar num
|
|
A negative decimal number representing the
|
|
command that was executed
|
|
.Ar num
|
|
of
|
|
commands previously.
|
|
For example, \-1 is the immediately previous command.
|
|
.It Ar string
|
|
A string indicating the most recently entered command
|
|
that begins with that string.
|
|
If the
|
|
.Ar old Ns = Ns Ar new
|
|
operand is not also specified with
|
|
.Fl s ,
|
|
the string form of the first operand cannot contain an embedded equal sign.
|
|
.El
|
|
.El
|
|
.Pp
|
|
The following variables affect the execution of
|
|
.Ic fc :
|
|
.Bl -tag -width ".Va HISTSIZE"
|
|
.It Va FCEDIT
|
|
Name of the editor to use for history editing.
|
|
.It Va HISTSIZE
|
|
The number of previous commands that are accessible.
|
|
.El
|
|
.It Ic fg Op Ar job
|
|
Move the specified
|
|
.Ar job
|
|
or the current job to the foreground.
|
|
.It Ic getopts Ar optstring var
|
|
The
|
|
.Tn POSIX
|
|
.Ic getopts
|
|
command.
|
|
The
|
|
.Ic getopts
|
|
command deprecates the older
|
|
.Xr getopt 1
|
|
command.
|
|
The first argument should be a series of letters, each possibly
|
|
followed by a colon which indicates that the option takes an argument.
|
|
The specified variable is set to the parsed option.
|
|
The index of
|
|
the next argument is placed into the shell variable
|
|
.Va OPTIND .
|
|
If an option takes an argument, it is placed into the shell variable
|
|
.Va OPTARG .
|
|
If an invalid option is encountered,
|
|
.Ar var
|
|
is set to
|
|
.Ql \&? .
|
|
It returns a false value (1) when it encounters the end of the options.
|
|
A new set of arguments may be parsed by assigning
|
|
.Li OPTIND=1 .
|
|
.It Ic hash Oo Fl rv Oc Op Ar command ...
|
|
The shell maintains a hash table which remembers the locations of commands.
|
|
With no arguments whatsoever, the
|
|
.Ic hash
|
|
command prints out the contents of this table.
|
|
.Pp
|
|
With arguments, the
|
|
.Ic hash
|
|
command removes each specified
|
|
.Ar command
|
|
from the hash table (unless they are functions) and then locates it.
|
|
With the
|
|
.Fl v
|
|
option,
|
|
.Ic hash
|
|
prints the locations of the commands as it finds them.
|
|
The
|
|
.Fl r
|
|
option causes the
|
|
.Ic hash
|
|
command to delete all the entries in the hash table except for functions.
|
|
.It Ic jobid Op Ar job
|
|
Print the process IDs of the processes in the specified
|
|
.Ar job .
|
|
If the
|
|
.Ar job
|
|
argument is omitted, use the current job.
|
|
.It Ic jobs Oo Fl lps Oc Op Ar job ...
|
|
Print information about the specified jobs, or all jobs if no
|
|
.Ar job
|
|
argument is given.
|
|
The information printed includes job ID, status and command name.
|
|
.Pp
|
|
If the
|
|
.Fl l
|
|
option is specified, the PID of each job is also printed.
|
|
If the
|
|
.Fl p
|
|
option is specified, only the process IDs for the process group leaders
|
|
are printed, one per line.
|
|
If the
|
|
.Fl s
|
|
option is specified, only the PIDs of the job commands are printed, one per
|
|
line.
|
|
.It Ic kill
|
|
A built-in equivalent of
|
|
.Xr kill 1
|
|
that additionally supports sending signals to jobs.
|
|
.It Ic local Oo Ar variable ... Oc Op Fl
|
|
See the
|
|
.Sx Functions
|
|
subsection.
|
|
.It Ic printf
|
|
A built-in equivalent of
|
|
.Xr printf 1 .
|
|
.It Ic pwd Op Fl L | P
|
|
Print the path of the current directory.
|
|
The built-in command may
|
|
differ from the program of the same name because the
|
|
built-in command remembers what the current directory
|
|
is rather than recomputing it each time.
|
|
This makes
|
|
it faster.
|
|
However, if the current directory is
|
|
renamed,
|
|
the built-in version of
|
|
.Xr pwd 1
|
|
will continue to print the old name for the directory.
|
|
.Pp
|
|
If the
|
|
.Fl P
|
|
option is specified, symbolic links are resolved.
|
|
If the
|
|
.Fl L
|
|
option is specified, the shell's notion of the current directory
|
|
is printed (symbolic links are not resolved).
|
|
This is the default.
|
|
.It Ic read Oo Fl p Ar prompt Oc Oo
|
|
.Fl t Ar timeout Oc Oo Fl er Oc Ar variable ...
|
|
The
|
|
.Ar prompt
|
|
is printed if the
|
|
.Fl p
|
|
option is specified
|
|
and the standard input is a terminal.
|
|
Then a line is
|
|
read from the standard input.
|
|
The trailing newline
|
|
is deleted from the line and the line is split as
|
|
described in the section on
|
|
.Sx White Space Splitting (Field Splitting)
|
|
above, and
|
|
the pieces are assigned to the variables in order.
|
|
If there are more pieces than variables, the remaining
|
|
pieces (along with the characters in
|
|
.Va IFS
|
|
that separated them)
|
|
are assigned to the last variable.
|
|
If there are more variables than pieces, the remaining
|
|
variables are assigned the null string.
|
|
.Pp
|
|
Backslashes are treated specially, unless the
|
|
.Fl r
|
|
option is
|
|
specified.
|
|
If a backslash is followed by
|
|
a newline, the backslash and the newline will be
|
|
deleted.
|
|
If a backslash is followed by any other
|
|
character, the backslash will be deleted and the following
|
|
character will be treated as though it were not in
|
|
.Va IFS ,
|
|
even if it is.
|
|
.Pp
|
|
If the
|
|
.Fl t
|
|
option is specified and the
|
|
.Ar timeout
|
|
elapses before a complete line of input is supplied,
|
|
the
|
|
.Ic read
|
|
command will return an exit status as if terminated by
|
|
.Dv SIGALRM
|
|
without assigning any values.
|
|
The
|
|
.Ar timeout
|
|
value may optionally be followed by one of
|
|
.Ql s ,
|
|
.Ql m
|
|
or
|
|
.Ql h
|
|
to explicitly specify seconds, minutes or hours.
|
|
If none is supplied,
|
|
.Ql s
|
|
is assumed.
|
|
.Pp
|
|
The
|
|
.Fl e
|
|
option exists only for backward compatibility with older scripts.
|
|
.Pp
|
|
The exit status is 0 on success, 1 on end of file,
|
|
between 2 and 128 if an error occurs
|
|
and greater than 128 if a trapped signal interrupts
|
|
.Ic read .
|
|
.It Ic readonly Oo Fl p Oc Op Ar name ...
|
|
Each specified
|
|
.Ar name
|
|
is marked as read only,
|
|
so that it cannot be subsequently modified or unset.
|
|
The shell allows the value of a variable to be set
|
|
at the same time as it is marked read only
|
|
by using the following form:
|
|
.Pp
|
|
.D1 Ic readonly Ar name Ns = Ns Ar value
|
|
.Pp
|
|
With no arguments the
|
|
.Ic readonly
|
|
command lists the names of all read only variables.
|
|
If the
|
|
.Fl p
|
|
option is specified, the read-only variables are printed as
|
|
.Dq Ic readonly Ar name Ns = Ns Ar value
|
|
lines, suitable for re-input to the shell.
|
|
.It Ic return Op Ar exitstatus
|
|
See the
|
|
.Sx Functions
|
|
subsection.
|
|
.It Ic set Oo Fl /+abCEefIimnpTuVvx Oc Oo Fl /+o Ar longname Oc Oo
|
|
.Fl c Ar string Oc Op Fl - Ar arg ...
|
|
The
|
|
.Ic set
|
|
command performs three different functions:
|
|
.Bl -item
|
|
.It
|
|
With no arguments, it lists the values of all shell variables.
|
|
.It
|
|
If options are given,
|
|
either in short form or using the long
|
|
.Dq Fl /+o Ar longname
|
|
form,
|
|
it sets or clears the specified options as described in the section called
|
|
.Sx Argument List Processing .
|
|
.It
|
|
If the
|
|
.Dq Fl -
|
|
option is specified,
|
|
.Ic set
|
|
will replace the shell's positional parameters with the subsequent
|
|
arguments.
|
|
If no arguments follow the
|
|
.Dq Fl -
|
|
option,
|
|
all the positional parameters will be cleared,
|
|
which is equivalent to executing the command
|
|
.Dq Li "shift $#" .
|
|
The
|
|
.Dq Fl -
|
|
flag may be omitted when specifying arguments to be used
|
|
as positional replacement parameters.
|
|
This is not recommended,
|
|
because the first argument may begin with a dash
|
|
.Pq Ql -
|
|
or a plus
|
|
.Pq Ql + ,
|
|
which the
|
|
.Ic set
|
|
command will interpret as a request to enable or disable options.
|
|
.El
|
|
.It Ic setvar Ar variable value
|
|
Assigns the specified
|
|
.Ar value
|
|
to the specified
|
|
.Ar variable .
|
|
The
|
|
.Ic setvar
|
|
command is intended to be used in functions that
|
|
assign values to variables whose names are passed as parameters.
|
|
In general it is better to write
|
|
.Dq Ar variable Ns = Ns Ar value
|
|
rather than using
|
|
.Ic setvar .
|
|
.It Ic shift Op Ar n
|
|
Shift the positional parameters
|
|
.Ar n
|
|
times, or once if
|
|
.Ar n
|
|
is not specified.
|
|
A shift sets the value of
|
|
.Li $1
|
|
to the value of
|
|
.Li $2 ,
|
|
the value of
|
|
.Li $2
|
|
to the value of
|
|
.Li $3 ,
|
|
and so on,
|
|
decreasing the value of
|
|
.Li $#
|
|
by one.
|
|
For portability, shifting if there are zero positional parameters
|
|
should be avoided, since the shell may abort.
|
|
.It Ic test
|
|
A built-in equivalent of
|
|
.Xr test 1 .
|
|
.It Ic times
|
|
Print the amount of time spent executing the shell process and its children.
|
|
The first output line shows the user and system times for the shell process
|
|
itself, the second one contains the user and system times for the
|
|
children.
|
|
.It Ic trap Oo Ar action Oc Ar signal ...
|
|
.It Ic trap Fl l
|
|
Cause the shell to parse and execute
|
|
.Ar action
|
|
when any specified
|
|
.Ar signal
|
|
is received.
|
|
The signals are specified by name or number.
|
|
In addition, the pseudo-signal
|
|
.Cm EXIT
|
|
may be used to specify an
|
|
.Ar action
|
|
that is performed when the shell terminates.
|
|
The
|
|
.Ar action
|
|
may be an empty string or a dash
|
|
.Pq Ql - ;
|
|
the former causes the specified signal to be ignored
|
|
and the latter causes the default action to be taken.
|
|
Omitting the
|
|
.Ar action
|
|
and using only signal numbers is another way to request the default action.
|
|
In a subshell or utility environment,
|
|
the shell resets trapped (but not ignored) signals to the default action.
|
|
The
|
|
.Ic trap
|
|
command has no effect on signals that were ignored on entry to the shell.
|
|
.Pp
|
|
Option
|
|
.Fl l
|
|
causes the
|
|
.Ic trap
|
|
command to display a list of valid signal names.
|
|
.It Ic true
|
|
A null command that returns a 0 (true) exit value.
|
|
.It Ic type Op Ar name ...
|
|
Interpret each
|
|
.Ar name
|
|
as a command and print the resolution of the command search.
|
|
Possible resolutions are:
|
|
shell keyword, alias, special shell builtin, shell builtin, command,
|
|
tracked alias
|
|
and not found.
|
|
For aliases the alias expansion is printed;
|
|
for commands and tracked aliases
|
|
the complete pathname of the command is printed.
|
|
.It Ic ulimit Oo Fl HSabcdfklmnpstuvw Oc Op Ar limit
|
|
Set or display resource limits (see
|
|
.Xr getrlimit 2 ) .
|
|
If
|
|
.Ar limit
|
|
is specified, the named resource will be set;
|
|
otherwise the current resource value will be displayed.
|
|
.Pp
|
|
If
|
|
.Fl H
|
|
is specified, the hard limits will be set or displayed.
|
|
While everybody is allowed to reduce a hard limit,
|
|
only the superuser can increase it.
|
|
The
|
|
.Fl S
|
|
option
|
|
specifies the soft limits instead.
|
|
When displaying limits,
|
|
only one of
|
|
.Fl S
|
|
or
|
|
.Fl H
|
|
can be given.
|
|
The default is to display the soft limits,
|
|
and to set both the hard and the soft limits.
|
|
.Pp
|
|
Option
|
|
.Fl a
|
|
causes the
|
|
.Ic ulimit
|
|
command to display all resources.
|
|
The parameter
|
|
.Ar limit
|
|
is not acceptable in this mode.
|
|
.Pp
|
|
The remaining options specify which resource value is to be
|
|
displayed or modified.
|
|
They are mutually exclusive.
|
|
.Bl -tag -width indent
|
|
.It Fl b Ar sbsize
|
|
The maximum size of socket buffer usage, in bytes.
|
|
.It Fl c Ar coredumpsize
|
|
The maximal size of core dump files, in 512-byte blocks.
|
|
.It Fl d Ar datasize
|
|
The maximal size of the data segment of a process, in kilobytes.
|
|
.It Fl f Ar filesize
|
|
The maximal size of a file, in 512-byte blocks.
|
|
.It Fl k Ar kqueues
|
|
The maximal number of kqueues
|
|
(see
|
|
.Xr kqueue 2 )
|
|
for this user ID.
|
|
.It Fl l Ar lockedmem
|
|
The maximal size of memory that can be locked by a process, in
|
|
kilobytes.
|
|
.It Fl m Ar memoryuse
|
|
The maximal resident set size of a process, in kilobytes.
|
|
.It Fl n Ar nofiles
|
|
The maximal number of descriptors that could be opened by a process.
|
|
.It Fl p Ar pseudoterminals
|
|
The maximal number of pseudo-terminals for this user ID.
|
|
.It Fl s Ar stacksize
|
|
The maximal size of the stack segment, in kilobytes.
|
|
.It Fl t Ar time
|
|
The maximal amount of CPU time to be used by each process, in seconds.
|
|
.It Fl u Ar userproc
|
|
The maximal number of simultaneous processes for this user ID.
|
|
.It Fl v Ar virtualmem
|
|
The maximal virtual size of a process, in kilobytes.
|
|
.It Fl w Ar swapuse
|
|
The maximum amount of swap space reserved or used for this user ID,
|
|
in kilobytes.
|
|
.El
|
|
.It Ic umask Oo Fl S Oc Op Ar mask
|
|
Set the file creation mask (see
|
|
.Xr umask 2 )
|
|
to the octal or symbolic (see
|
|
.Xr chmod 1 )
|
|
value specified by
|
|
.Ar mask .
|
|
If the argument is omitted, the current mask value is printed.
|
|
If the
|
|
.Fl S
|
|
option is specified, the output is symbolic, otherwise the output is octal.
|
|
.It Ic unalias Oo Fl a Oc Op Ar name ...
|
|
The specified alias names are removed.
|
|
If
|
|
.Fl a
|
|
is specified, all aliases are removed.
|
|
.It Ic unset Oo Fl fv Oc Ar name ...
|
|
The specified variables or functions are unset and unexported.
|
|
If the
|
|
.Fl v
|
|
option is specified or no options are given, the
|
|
.Ar name
|
|
arguments are treated as variable names.
|
|
If the
|
|
.Fl f
|
|
option is specified, the
|
|
.Ar name
|
|
arguments are treated as function names.
|
|
.It Ic wait Op Ar job ...
|
|
Wait for each specified
|
|
.Ar job
|
|
to complete and return the exit status of the last process in the
|
|
last specified
|
|
.Ar job .
|
|
If any
|
|
.Ar job
|
|
specified is unknown to the shell, it is treated as if it
|
|
were a known job that exited with exit status 127.
|
|
If no operands are given, wait for all jobs to complete
|
|
and return an exit status of zero.
|
|
.El
|
|
.Ss Commandline Editing
|
|
When
|
|
.Nm
|
|
is being used interactively from a terminal, the current command
|
|
and the command history
|
|
(see
|
|
.Ic fc
|
|
in
|
|
.Sx Built-in Commands )
|
|
can be edited using
|
|
.Nm vi Ns -mode
|
|
command line editing.
|
|
This mode uses commands similar
|
|
to a subset of those described in the
|
|
.Xr vi 1
|
|
man page.
|
|
The command
|
|
.Dq Li "set -o vi"
|
|
(or
|
|
.Dq Li "set -V" )
|
|
enables
|
|
.Nm vi Ns -mode
|
|
editing and places
|
|
.Nm
|
|
into
|
|
.Nm vi
|
|
insert mode.
|
|
With
|
|
.Nm vi Ns -mode
|
|
enabled,
|
|
.Nm
|
|
can be switched between insert mode and command mode by typing
|
|
.Aq ESC .
|
|
Hitting
|
|
.Aq return
|
|
while in command mode will pass the line to the shell.
|
|
.Pp
|
|
Similarly, the
|
|
.Dq Li "set -o emacs"
|
|
(or
|
|
.Dq Li "set -E" )
|
|
command can be used to enable a subset of
|
|
.Nm emacs Ns -style
|
|
command line editing features.
|
|
.Sh ENVIRONMENT
|
|
The following environment variables affect the execution of
|
|
.Nm :
|
|
.Bl -tag -width ".Ev LANGXXXXXX"
|
|
.It Ev ENV
|
|
Initialization file for interactive shells.
|
|
.It Ev LANG , Ev LC_*
|
|
Locale settings.
|
|
These are inherited by children of the shell,
|
|
and is used in a limited manner by the shell itself.
|
|
.It Ev PWD
|
|
An absolute pathname for the current directory,
|
|
possibly containing symbolic links.
|
|
This is used and updated by the shell.
|
|
.It Ev TERM
|
|
The default terminal setting for the shell.
|
|
This is inherited by children of the shell, and is used in the history
|
|
editing modes.
|
|
.El
|
|
.Pp
|
|
Additionally, environment variables are turned into shell variables
|
|
at startup,
|
|
which may affect the shell as described under
|
|
.Sx Special Variables .
|
|
.Sh FILES
|
|
.Bl -tag -width "/etc/suid_profileXX" -compact
|
|
.It Pa ~/.profile
|
|
User's login profile.
|
|
.It Pa /etc/profile
|
|
System login profile.
|
|
.It Pa /etc/shells
|
|
Shell database.
|
|
.It Pa /etc/suid_profile
|
|
Privileged shell profile.
|
|
.El
|
|
.Sh EXIT STATUS
|
|
Errors that are detected by the shell, such as a syntax error, will
|
|
cause the shell to exit with a non-zero exit status.
|
|
If the shell is not an interactive shell, the execution of the shell
|
|
file will be aborted.
|
|
Otherwise the shell will return the exit status of the last command
|
|
executed, or if the
|
|
.Ic exit
|
|
builtin is used with a numeric argument, it
|
|
will return the argument.
|
|
.Sh SEE ALSO
|
|
.Xr builtin 1 ,
|
|
.Xr chsh 1 ,
|
|
.Xr echo 1 ,
|
|
.Xr ed 1 ,
|
|
.Xr emacs 1 ,
|
|
.Xr kill 1 ,
|
|
.Xr printf 1 ,
|
|
.Xr pwd 1 ,
|
|
.Xr test 1 ,
|
|
.Xr vi 1 ,
|
|
.Xr execve 2 ,
|
|
.Xr getrlimit 2 ,
|
|
.Xr umask 2 ,
|
|
.Xr wctype 3 ,
|
|
.Xr editrc 5 ,
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.Xr shells 5
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.Sh HISTORY
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A
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.Nm
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command, the Thompson shell, appeared in
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.At v1 .
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It was superseded in
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.At v7
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by the Bourne shell, which inherited the name
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.Nm .
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.Pp
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This version of
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.Nm
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was rewritten in 1989 under the
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.Bx
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license after the Bourne shell from
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.At V.4 .
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.Sh AUTHORS
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This version of
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.Nm
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was originally written by
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.An Kenneth Almquist .
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.Sh BUGS
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The
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.Nm
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utility does not recognize multibyte characters other than UTF-8.
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Splitting using
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.Va IFS
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does not recognize multibyte characters.
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